The answer is he made a pilgrimage to Mecca and brought Islamic teachings back to Mali.
This is incorrect. Mansa Musa was a devout Muslim and did not bring Christianity to East Africa. Christianity was already present in parts of East Africa, such as Ethiopia, long before Mansa Musa's time.
This is incorrect. Axum was a kingdom in what is now Ethiopia, and its religious practices were separate from those of Mali. Mansa Musa was focused on promoting Islam, not the gods of Axum.
This is incorrect. While the Mali Empire did have interactions with the Songhai Empire, Mansa Musa is not known for taking over Songhai. The Songhai Empire rose to prominence after the decline of the Mali Empire.
This is correct. Mansa Musa is most famous for his pilgrimage (Hajj) to Mecca in 1324. During this journey, he displayed immense wealth and generosity, which brought attention to the Mali Empire. Upon his return, he brought back Islamic scholars, architects, and books, which significantly influenced the cultural and educational development of Mali.